Dual mode rocket propulsion systems and dual mode rocket engines (also referred to as thrusters) are known in the art. Currently, many spacecraft use dual-mode propulsion systems, with bipropellant engines for larger thrust operations, and monopropellant engines for smaller thrust or when minimum impulse bit is important. In the art the choice of propellants which are suitable in both bipropellant and monopropellant engines are limited to a few very hazardous propellants. Such bipropellants comprise hydrazine or a derivative thereof, such as monomethyl hydrazine (MMH) and unsymmetrical dimethyl hydrazine (UDMH). An example of a dual mode thruster is a thruster referred to as a Secondary Combustion Augmented Thruster (SCAT). A bipropellant dual mode rocket propulsion system comprising a bipropellant thruster having dual mode capability (i.e. ability to operate either in monopropellant mode or in bipropellant mode) has been described in e.g. U.S. Pat. No. 6,135,393, wherein hydrazine is used as the fuel, and, preferably, nitrogen tetroxide (NTO) as the oxidizer.
The mission requirements for a particular propulsion system requiring high performance are defined by a set of figures of merit. One of the most important figures of merit is specific impulse (Isp) as it indicates the maximum velocity changes that the spacecraft can achieve, which is the very objective of such propulsion system. Specific impulse is defined as the thrust developed by an engine per unit of propellant mass flow rate. If the thrust is measured in Newton (N) and the flow rate is measured in kilograms (kg) per second (s), then the unit of measurement of specific impulse is Ns/kg. For medium to large spacecraft with requirements of significant velocity changes this is the most important parameter. For small spacecraft where dimensions may be limiting, the density impulse, i.e. Ns per propellant volume, may be the dominant figure of merit. Another figure of merit is the thrust of a rocket engine as it determines how long a maneuver will take and what acceleration it will provide. Yet another parameter is the smallest or minimum impulse bit (Ns) that the engine can generate as it determines how precise a maneuver can be performed.
Both hydrazine (fuel) and nitrogen tetroxide (oxidizer), and their derivatives are extremely hazardous for humans as they are highly toxic, carcinogenic, corrosive, etc., and they are associated with significant concerns regarding the severe impact on the environment that they can cause in the case of spillage and emissions. Therefore, the handling thereof and the safety requirements are extremely demanding, time consuming and costly.
The ECHA (European Chemicals Agency) has within REACH (Registration, Evaluation, Authorisation and restriction of Chemicals), which is the European Community Regulation on chemicals and their safe use, identified hydrazine as a substance of very high concern which may lead to that hydrazine may be banned for use in new development. Clean Space, which is an initiative by the European Space Agency (ESA), also calls for substituting conventional hazardous propellants.
There is also a new law, Space Operations Act, in France, with respect to space debris, which requires that the spacecraft shall be deorbited when no longer in use.
A significant achievement in the art is the feasibility to substitute hydrazine as a monopropellant for many space applications. This has been successfully demonstrated using the HPGP® technology comprising the LMP-103S monopropellant blend (described in e.g. WO 2012/166046) and corresponding thrusters (disclosed in e.g. WO 02/095207) ranging from typically 0.5 N to 200 N. A 1 N HPGP® propulsion system has been operational for several years in an earth orbit in space on the main PRISMA satellite.
Accordingly, it is therefore desirable to provide a dual mode propulsion system avoiding the use of hydrazine, nitrogen tetroxide, and derivatives thereof. However, so far, no viable rocket propulsion systems, rocket engines, and corresponding alternative propellants with performance comparable to the prior art hazardous hydrazine propellants have been realized.